tools/mesh-cfgclient: Add timeout for expected response

tools/mesh-cfgclient: Add timeout for expected response

This adds a pending request queue for the issued commands awaiting
response from a remote config server. The tool forces "single-issue"
of a config command, i.e. only one command that has a specified return
type is allowed to be outstanding per a remote node address.
That is, if AppKeyAdd command to a node is pending response, the tool
disallows sending another AppKeyAdd, AppKeyUpdate or AppKeyDelete to
the same address until response timeout expires (notification will
be displayed).
The default response timeout is set to 2 seconds and is configurable
by "timeout" command.

Change-Id: I4611df3e02faf1a5310faec16cd714f7cde5d013
Signed-off-by: Anupam Roy <anupam.r@samsung.com>